Experimental study and numerical simulation of partial discharges in deformed bubbles in transformer oil

The experiments on partial discharges (PDs) in gas bubbles floating up in transformer oil and calculations of the characteristics of partial discharge (PD) in the bubbles were made. For floating up bubbles, it was shown that the PD did not occur even if the electric field was higher than that obtained from Pashen's law. The experiments on inception of PD in bubbles with X-rays were performed. They confirmed our hypothesis that the absence of PDs can be explained by the lack of initial electrons in floating up bubbles at the conditions of low radiation background. The calculations of the “apparent” and “true” charges of PD in elliptic cavities in a condensed dielectric were performed. A good agreement of the simulations with our experiments was revealed. For the elliptic bubbles, the “apparent” charge is proportional to the bubble volume while the “true” charge is proportional to the surface of the bubble.